In the field of high voltage power conversion, there are a number of methods that can be employed to design a single polarity solid state shunt regulator that is controlled from a low voltage signal. However, in some applications, a regulator is required to accept a high voltage input that has a changing polarity relative to ground and regulate the output to a given magnitude of the same polarity as the input. Typically, circuitry designed around vacuum tube technology has been used to satisfy this requirement.
An example of a single polarity shunt regulator is provided in U.S. Pat. No. 6,222,350 to Mosley (xe2x80x9cthe Mosley referencexe2x80x9d). The high voltage shunt regulator including a series of Zener diodes connected in series with a thermal compensation circuit that includes a plurality of MOSFET switches and resistive voltage dividers. When a voltage in excess of the Zener threshold voltage is applied to the series of Zener diodes from a high voltage source, the Zener diodes conduct substantially all of the current applied at the input terminal to the output terminal. However, because the threshold voltage of a Zener diode decreases as the temperature of the Zener diode increases (which happens as the Zener diode conducts current), the MOSFETs of the thermal compensation circuit must be engaged to provide a compensatory voltage drop so that the diversion of current takes place at the appropriate voltage level. U.S. Pat. No. 5,949,122 to Sccaccionoce discloses a similar system using bipolar junction transistors instead of MOSFETs. Although these references discuss the use of shunt regulators in high voltage applications, the disclosed regulators are unsuitable for use in dual polarity applications. Accordingly, neither discusses the need for quick switching to accommodate changes in the polarity of the high voltage source.